Melt blown roving die

ABSTRACT

A roving of entangled and self-bonded fine fibers of thermoplastic resins may be formed by a melt blown roving technique which comprises extruding the thermoplastic resin through a die having the die openings in a circle into a hot gas stream to attenuate the extruded polymer into fibers in the form of a cone of fibers in space and collecting the fibers as a tow. The process yields many unique products which vary in characteristics depending on the specific collection of the fibers.

United States Patent [15] 3,684,415 Buntin et al. [451 Aug. 15, 1972 [54] MELT BLOWN ROVING DIE 1,933,587 11/1933 Dreyfus et a1. 18/8 QD X Inventors: R. w-

Francis James Keller; vome Murdock 2,991,507 7/1961 bev ecque et a1 ..65/5 X a of Baytown Tex 3,017,664 1/1962 Ladlsch ..264/D1G. 75 3,333,040 7/1967 Nakahara ..l56/167 X Asslgneel Fsso Research and gi i g 3,433,857 3/1969 Dutton et a1 ..l56/167 X p y 3,439,085 4/1969 Hartmann ..l56/ 167 X F' 7 [22] Dec l9 0 Primary Examiner-J. Spencer Overholser PP N06 98,523 Assistant Examiner-Michael 0. Sutton Attorney-Thomas B. McCulloch, Timothy L. Bur- Related Apphcahon Data gess, Melvin F. Fincke, Jonn S. Schneider and Syl- [62] Division of Ser. No. 752,592, Aug. 14, 1968, vester W. Brock, Jr.

Pat. No. 3,615,995.

[57] ABSTRACT [52] s i i A roving of entangled and self-bonded fine fibers of [51] Int Cl 1329 3/04 thermoplastic resins may be formed by a melt blown 58] Fie'ld 18/1 roving technique which comprises extruding the ther- 18/8 QM 8 SR 8 WE moplastic resin through a die having the die openings v 8 8 SC N M 264mm in a circle into a hot gas stream to attenuate the ex- 19750. SM CF 65/5 truded polymer into fibers in the form of a cone of fibers in space and collecting the fibers as a tow. The process yields many unique products which vary in [56] References Cited characteristics depending on the specific collection of UNITED STATES PATENTS the fibers- 2,51 1,381 6/ 1950 Stevens ..65/5 8 Clains, 6 Drawing Figures POLYMER FROM EXTRUDER ANNULA AIR ANNULAR POLYMER PASSAGE V 22 PASSAGE HOT AIR ANNULAR AIR x- PASSAGE PATENTEWGS BEST AVAIL-ABLE COPY 8684L4l5 SHEET 1 [IF 3 m. JUwQOF INVENTORS. ROBERT R. BUNTIN, JOHN W HARDING, JAMES P. KELLER,

VOLLIE L. MURDOCK,

MM AT ORNEY.

PATENTEDAUSIS 1912 SHEET 2 [IF 3 mum;

ATTORNEY.

PATENTEDms 15 m2 sum 3 0r FIG. 6.

| INVENTORS. 4 I ROBERT R. BUNTIN,

I JOHN w. HARDING, JAMES P. KELLER,

VOLLIE L. MURDOCK,

M w a ATTORNEY.

1 MELT BLOWN ROVING DIE CROSS REFERENCE TO RELATED APPLICATION This application is a division of Ser. No. 752,592 filed Aug. 14, 1968, entitled Process for Melt Blown Roving", now US. Pat. No. 3,615,995.

BACKGROUND OF THE INVENTION Most thermoplastic resins are'extruded to form fibers. For example, polypropylene fibers are formed by conventional melt spinning techniques with subsequent drawing, crimping, twisting, texturizing and the like to produce the polypropylene fibers in a final desired form. The purpose of the process of the present invention is to continuously convert thermoplastic resins such as polypropylene into a roving of entangled and self-bonded fine fibers by a melt blown roving technique.

In considering some of the processes of the prior art which disclose the formation of a cylindrical tow of fibers, the following US. Pat. Nos. have been considered: 2,736,676, 2,886,877, 3,023,075, 3,148,101, 3,433,857, and 3,439,085.

SUMMARY OF THE INVENTION The present invention is directed to the extrusion of thermoplastic resins into a roving of fine fibers by extruding the resin through a die having the die openings arranged in a circle. Gas streams, preferably air, are supplied by gas plenums in the form of slots concentrically inside and outside of the circle of die openings to attenuate the extruded resin into fine fibers. The circle of die openings are preferably arranged in the die so as to extrude and direct the thermoplastic resin as a cone of fibers in space extending from the die openings, the cone being largest at the die and narrowing to an imaginary focal point in front of the die. The shape of the cone of fibers in space may be modified by controlling the relative velocities of the gas streams from the plenums inside and outside the circle of die openings to change the distance of the imaginary focal point of the cone of fibers in front of the die.

The conical profile of the fibers coming from the die openings may be further controlled by means of an auxiliary gas stream supplied through a gas plenum in the form of a jet in the center of the circle of die openings. The auxiliary gas stream assists in cooling the fibers prior to collection and also modifies the laydown of the fibers. Thus, the auxiliary gas stream may be used to change the conical shape of the fibers as they are attenuated from the die so that the profile of the fibers in space becomes more cylindrical at the laydown zone. By thus controlling the auxiliary gas stream the timetemperature history of the extruded resin may be changed as well as the laydown pattern of the individual fibers.

The fibers may be collected as a roving in a number of distinct ways. The fibers may be collected either by moving the roving of fibers away from the die or through the center of the circle of die openings. The direction of removal of the roving of fibers formed are distinguished by defining forward takeoff as collecting and moving the roving in a direction away from the die and reverse takeofi as collecting and moving the roving of fibers back through the center of the circle of die openings. The direction of collecting and moving the roving results in the production of distinctly different products. For example, in the reverse takeoff a smooth skin of bonded fibers may be produced on the outside of the roving, while on the other hand, forward takeoff produces a softer outer layer of individual fibers and aggregates of fibers on the roving.

A fixed or rotating collecting means may be used in the laydown zone to collect the fine fibers in a desired form. The preferred collecting means is a stabilizer rod. The stabilizer rod is preferably rotated to produce a uniform tow. The rotation of the stabilizer rod produces a permanent twist in the product and eliminates the opening or soft center of the tow due to being removed from the stabilizer rod. However, if a hollow tow is desired a large stationary or rotating rod may be used.

Further, the tow of entangled and self-bonded fibers may be modified by using more than one die. Thus, a tow may have additional fibers bonded to the outside by passing the tow through one or more dies and using the tow as the collecting means for collecting further fibers in place of the stabilizer rod. The direction of takeoff as the tow passes through the circle of die openings in each die will determine the overall nature of the tow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of the overall melt blown roving process with reverse takeofl;

FIG. 2 is a cross-sectional detail of tions cut away;

FIG. 3 is a detail of the inner ring of the die;

FIG. 4 is an enlarged view of the die to illustrate the collecting or laydown zone;

FIG. 5 is a schematic view of the melt blown roving process with forward takeofl';

FIG. 6 is a schematic view of the melt blown roving process with a plurality of dies.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 which sets forth one embodiment of the overall melt blown roving process, a thermoplastic such a polypropylene is introduced into the feed hopper 1 of an extruder 2. The thermoplastic is heated in the extruder 2 and is placed under shear by a screw (not shown) in the extruder 2 driven by drive 3. The thermoplastic is extruded from a die 4 which has a plurality of die openings 5 arranged in a circle into a gas stream. The gas stream is supplied by gas plenums 6 and 7 arranged concentrically inside and outside, respectively, to the circle of die openings 5.

The thermoplastic is extruded from the die 4 as continuous fibers which are attenuated by the gas stream from plenums 6 and 7. Gas is supplied to the plenums 6 and 7 by lines 8 and 9, respectively, each of which may be independently controlled as to pressure and temperature (not shown). By the control of the gas stream, the extruded fibers are attenuated from the die openings 5 in the shape of a cone, with the largest portion of the cone being at the die openings 5. The fibers are collected in a laydown zone 10 which is in proximity to the imaginary apex of the cone of attenuated fibers. The distance from the die openings 5 to the a die with porlaydown zone is controlled to a large extent by the relative gas velocities from plenums 6 and 7.

The attenuated fibers are collected on a collecting device 11 which may have various shapes and sizes. The collecting device ll. is preferably a stabilizer rod 12 which is held stationary or rotated. The stabilizer rod 12 may be placed through the center of a funnel 13 or other means which act as a bearing to stabilize the rod 12 when rotated by a drive means 14. The funnel 13 also protects the drive means 14 from stray fine fibers. As the fibers collect on the stabilizer rod 12, they entangle and become self-bonded.

To modify the configuration of the fibers as they are collected in the laydown zone 10 on the stabilizer rod 12, an auxiliary gas stream may be supplied fiom a gas plenum 15 formed by a double wall pipe 16. The double wall pipe 16 is positioned along the axis defined by the center axis of the die 4 and the center of the circle of die openings 5. The gas stream from gas plenum 15 is directed at the collecting device 11 or stabilizer rod 12 and the air stream modifies the laydown of the fibers in laydown zone 10 so that they take a more cylindrical shape. Gas, preferably air, is supplied to the double wall pipe 16 by line 17 which may be controlled as to pressure and temperature. The auxiliary gas stream may be used to modify the time-temperature history of the fibers as well as the configuration and entanglement of the fibers. The gas supplied through gas plenum 15 may be cooler or hotter than the air supplied through plenums 6 and 7.

To begin the melt blow roving operation, a starter rod 18 is extended into the laydown zone 10 along the stabilizer rod l2to draw the fibers as a continuous tow from the stabilizer rod 12 either in a forward takeoff or in a reverse takeofi', the reverse takeofl' illustrated in FIG. 1. As shown in FIG. 1, the starter rod 18 is drawn 7 through the center of the double wall pipe 16 where the tow is attached to a windup reel 19 driven by motor 20.

In FIG. 2 and 3, the details of a die 4 are illustrated which may be used in the present invention. The die4 comprises a die assembly 21 which provides an inlet from the extruder 2 to an annular polymer distribution chamber 22 and a plurality of passageways to the die openings 5. The die 4 is torusoidal in shape, the term torusoidal" meaning herein a die assembly of any crosssectional shape which is rotated around an axis so that the die openings 5 of the die 4 are in a circle with the axis as the center. The die assembly 21 may be comprised of an inner ring member 23 and an outer ring member 24 which meet in a facing 25. A plurality of grooves 26 may be milled in the facing of either the inner ring member 23 or outer ring member 24 or in both facings to provide the passageways from the annular polymer chamber 22 to the die openings 5. An outer coverplate 27 which overlays the outer ring 24 defines the outer gas plenum 7 whose outlet is in the form of a slot concentrically outside the die openings 5. An inner coverplate 28 defines an inner gas plenum 6 whose outlet is in the form of a slot concentrically inside said die openings 5. A thermoplastic polymer is introduced into polymer inlet means '29 and is forced into the annular polymer chamber 22 and extruded through die openings 5. Hot gas, preferably air, is supplied by lines 8 and 9 into gas inlet means 30 and 31 which supply the gas under pressure to outer gas plenum 7 and inner gas plenum 6, respectively.

The shape of the cone of fibers as they are extruded and attenuated from the die openings 5 in the die 4 is controlled by the geometry of the die and by the relative velocities of the gas coming from the gas plenums 6 and 7. The gas plenums 6 and 7 may be built into the die 4 such that the angle alpha (or) between the two plenum outlets or slots 32 and 33 is up to but is preferably between 0 to 60. The plurality of passageways or grooves 26 in the die assembly 21 is at an angle beta (,8) which is smaller than the angle alpha (a) and at an angle between that defined by the gas plenums 6 and 7. Preferably the angle beta (B) is midway between the angle defined by the gas plenums 6 and 7. The geometry of the die is further defined in that the center line of the die openings 5 or grooves 26 and the axis of the die 4 define an angle delta (A) which may vary from 0 to 90 and is preferably 20 to 60. While the geometry of the die contributes to the shape of the cone of fibers as they leave the die openings 5, this shape may be immediately modified by the relative velocities of gas coming from the gas plenums 6 and 7 such that the angle gamma (1') between the fibers leaving the die openings 5 and the axis of the die may be within the range of 0 to 90 and preferably 20 to 60.

The collection of the fibers in the laydown zone 10 is more fully illustrated in FIG. 4 of the drawings. The melt blown roving operation of the present invention allows numerous products to be produced by varying the conditions in the laydown zone 10. The fibers are extruded and attenuated from the die openings 5 initially in the form of a cone A. As the fibers converge, the individual fibers come in contact with one another and with the roving previously formed. Being hot the fibers can stick or self-bond and begin to entangle. The fibers, however, continue to attenuate and stick together and to the roving further from the die openings 5 in the laydown zone 10 until a mass of entangled and self-bonded fibers is formed. The laydown zone 10 extends from the point where initial contact of fibers occur to the furthest point away from the die openings 5 where the fibers collect in the fiber mass as a tow. The laydown zone '10 may be several inches to a foot or so from the die openings 5. The laydown zone 10 may be modified by independently varying the angle gamma ('y) of the extruded thermoplastic, the use of the auxiliary gas stream from plenum 15 and the direction of takeoff. The use of the auxiliary gas stream from plenum 15 in most instances produces a more uniform laydown of the fibers and accordingly a more uniform tow of fibers is produced. When the tow 34 is removed from the laydown zone 10 by a reverse take ofi as illustrated in FIG. 4, the tow may have a bonded and smooth outer surface, whereas when the tow is removed from the laydown zone 10 in a forward takeoff, the outer surface appears more flufiy. A tow may be produced which is less dense and has less selfbonding by having the laydown zone 10 further away from the die openings 5.

Referring to FIG. 5, the melt blown roving technique of the present invention is illustrated with the forward takeoff. The thermoplastic resin is introduced into the feed hopper 41 of an extruder 42. The thermoplastic is heated, placed under shear by a screw in the extruder 42 driven by drive 43 and extruded from die 44 into-a gas stream. Die 44 has a plurality of die openings 45 arranged in a'circle. The gas stream is supplied by gas plenums 46 and 47 arranged concentrically inside and mixture of thermoplastic resins or a laminated tow may outside, respectively, to the circle of die openings 45. be formed of various resins. Further, additives or bini-ieated gas is supplied to the plenums 46 and 47 by ders may be incorporated into the roving by injection lines 48 and 49, respectively, each of which may be ininto one or more of the air streams. In this manner dependently controlled as to pressure and temperature. 5 composite structures can be formed with special, The extruded fibers are attenuated from the die desirable properties such as charcoal impregnated filter openings 45 by the gas stream and collected in a rods. laydown zone 50. The present invention will be further described by The collecting device preferred in the forward the following examples which illustrate the present intakeoff embodiment is a stabilizer rod 51 which is l vention but are not to be considered so as to limit the rotated by drive 52. The stabilizer rod 51 is inserted invention. v through the center of a double wall pipe 53 which sup- The following examples illustrate the operation of plies an auxiliary air stream from the gas plenum 54 the melt blown roving technique of the present invenwhich is defined by the double wall pipe 53. To begin tion. All samples were made using a 30 melt flow rate the operation, a starter rod 55 is placed in the laydown polypropylene r inzone 50 and is drawn away from the die 44 to form a tow 56. A tow 56 is wrapped around a windup reel 57 EXAMPLE 1 which is rotated byamotor 3- The following rovings or tows were made with in FIG. 6 the melt blown roving technique is illusreverse t k fi and with the conditions shown in the trated with a plurality of dies. By using two or more followi g table,

Stabilizer rod Polymer Free end A distance Product air, Temp., gm. to die, Varlae denier #lmin. F. min. in. setting Shape X10 .95 646 11.7 N.a. N.a. 9'16 x 1% round end -70 .92 668 11.4 8 18 54 :6 pointed 58.0

1. 662 20. 1 N.a. 20 34 x 9" pointed 53. 6

1. 69 672 17. 4 7 19 X x 9 round cnd 56. 0

" N.a.=Not available.

No'rE.Whr-.n the roducts were cut into short segments, they gave good even nppeurunce in the center with ii. slight soft honileil skin. When tested as c giirette filters, they gave total solids removiil COIIlpill'hbiu to or better than u Winston cigarette filter.

dies, tows may be produced having distinct and unusual EXAMPLE 2 properties The thermoplastic resin such as A 73 500 denier rovin was made by reverse takeoff Pdypmpyiene may be mmdmd 80 with the die at 680 F. aid air at 680 F. Main air rate and 90 of extruders 71, 81 and 91, respectively. The was I 6 lbs /min the auxiliary. air rate was 12 resin is extruded out of the dies 72, 82 and 92. As illuslbs lmi'n an the 1 er rate was 16 9 S [min The trated the first die 72 utilizes forward takeofl with a Ym gm 1/16 inch diameter stabilizer rod was terminated 8 stabilizer rod 73 rotated by motor 74. The tow 75 is inches from the die with a X 9 inch pointed blade. and IS passed thfough P double .f plpe 83' The variac was set as 20 for the rotation of the stabilpositioned along the axis of die 82. Additional fibers izer rod are bonded to the outside of tow 75 to produce a larger To he'at Sea] the Surface, the resulting roving or tow o 84 which P pass through a guard 82 was pulled through a die heated to -275 C. at speeds also Operated wlth forward takeoff T tow then of l to 6 ftJmin. The die had a short tapered entry with passed throilgh h double wall P posliloried a 9/32 inch channel, 1 inch long, at the exit. along the axis of die 92. The operation of die 92 is w1th The resulting product was a rigid rod consisting of a fevers? takeoff such that a Smooth bonded skm of fine, ropey, fiber core and acompacted, glazed surface fibers is produced on the outer surface of the tow 94. when collected at 6 ft'imin. At lower Speeds the Surface The tow 94 may be wound on areel (not shown). Wdhile became a solid plastic tube The rods could be cut the three dies 72, 82 and 92 have been illustrate as t two forward takeoff operations followed by a reverse cleanly ifd efi!tenng acuon' takeoff, it is understood that when more than one die is 5 used the possible combinations increase with the EXAWLE 3 number Ofdies used- Various hollow cylinders of fibrous material were In the melt blown roving tWhnique other the!" made by proper design of the stabilizer rod. The die moplastic resins y be used besides Polypropylene and main air were operated at 670 to 680 F. with a such as he ri nylons 66 and 610), P y y polymer flow rate of 12 to 20 gmslmin. The main and polyethylene terephthaiate, polymethylm ha y auxiliary air rates were adjusted to give stable perother polyolefins such as polyethylene, ethylene formance. propylene copolymers. By using a partitioned die or A $5 or /a-inch diameter tube was rotated as a stabilwhen more than one die is used more than one kind of izer rod. A large funnel, pointed toward the die, was thermoplastic resin may be used in the melt blown rovfixed coaxially on the tube. The system was operated ing process of the present invention. Thus, the roving with the funnel 6 to 15 inches from the die and with the characteristics are subject to modification by using a tube tip 0 to 12 inches from the die. With the assembly l EXAMPLE4 A roving was made, using the forward takeoffi process, which was subsequently drawn to yield 215 twine. The die was operated at 665 F., with the main! air at 684 F., and a polymer flow of 11.5 gmsJmin. The stabilizer rod had a %inch wide X 1 inch long blade at the end and projected about 15 inches in front of the die. With the stabilizer rod rotating at 1,700 rpm, a 20,000 denier roving was continuously withdrawn. The roving was subsequently fed at 4 ft/min and drawn 4/ l f in an oven held at 325 F.

The product was a fairly stifl, twisted, twine-like material with a tenacity of 1.8 gms/denier and an elongation to break of 15 percent.

With a die with 240 die openings on a circle having a diameter of 4 inches, polypropylene could be made into rovings under the following operable ranges:

+ Machine limits In the foregoing table of suitable operable ranges, the numbers set forth are not intended as absolute limits. Some numbers are indicated by the following mark which indicates the limits for the particular machine used in obtaining the number. The other numbers are merely set forth as suitable operating conditions and the exact limits have not been ascertained. Furthermore, the operable range for the operating conditions is expected to change as the size of the die is changed and other equipmentis umdtherewith.

The nature and objectsof the present ing been completely described and illustrated and the best mode thereof set forth,- what we wish to claim as new and useful and secure by Letters Patent is:

l. A die for the melt-blowing of fiber-forming thermoplastics which comprises in combination:

a. a generally toroidal-shaped support means with a large generally unobstructed center opening therein so constructed and adapted to receive a collecting means and having a system of inlet means and passageway means for said thermoplastic and means for supplying thermoplastic thereto and a system of inlet means and passageway means for a gaseous blowing agent and means for supplying the blowing agent thereto;

a plurality of die orifices arranged in a general circular configuration on one side of said toroidal support means generally surrounding said toroidal opening and connected with said thermoplastic passageway means;

first gas stream directing means concentric within said circle and connected with said gaseous blowing agent passageway means;

d. second gas stream directing means concentric without said circle and connected with said gaseous blowing agent passageway means;

said gas stream directing means being so adjusted and arranged as to attenuate said thermoplastic into fibers as it emerges from said orifices.

2. A die according to claim 1 wherein said toroidal support means compresses an inner ring member and an outer ring member which meet in a facing.

3. A die according to claim 2 wherein said inner ring member has a plurality of grooves milled in said facing to form the die openings.

4. A die according to claim 2 wherein said outer ring member has a plurality of grooves milled in said facing to form the die openings.

5. A die according to claim 1, which is further characterized by having a double-walled pipe extending through its center opening, so adjusted and arranged so as to permit gas flow between the two walls.

6. An apparatus for forming a roving from fiberforming thermoplastics which comprises in combination:

a. the die of claim 1;

b. a rod-shaped collecting means for said roving extending in a longitudinal direction through said center opening of said toroidal-shaped support means;

c. drive means for rotating said collecting means.

7. An apparatus according-to claim 6 which is farther characterized by having a roving take-up means.

8. An apparatus according to claim 6 which is further characterized by a starter sleeve means surrounding and encompassing said collecting means. 

1. A die for the melt-blowing of fiber-forming thermoplastics which comprises in combination: a. a generally toroidal-shaped support means with a large generally unobstructed center opening therein so constructed and adapted to receive a collecting means and having a system of inlet means and passageway means for said thermoplastic and means for supplying thermoplastic thereto and a system of inlet means and passageway means for a gaseous blowing agent and means for supplying the blowing agent thereto; b. a plurality of die orifices arranged in a general circular configuration on one side of said toroidal support means generally surrounding said toroidal opening and connected with said thermoplastic passageway means; c. first gas stream directing means concentric within said circle and connected with said gaseous blowing agent passageway means; d. second gas stream directing means concentric without said circle and connected with said gaseous blowing agent passageway means; said gas stream directing means being so adjusted and arranged as to attenuate said thermoplastic into fibers as it emerges from said orifices.
 2. A die according to claim 1 wherein said toroidal support means compresses an inner ring member and an outer ring member which meet in a facing.
 3. A die according to claim 2 wherein said inner ring member has a plurality of grooves milled in said facing to form the die openings.
 4. A die according to claim 2 wherein said outer ring member has a plurality of grooves milled in said facing to form the die openings.
 5. A die according to claim 1, which is further characterized by having a double-walled pipe extending through its center opening, so adjusted and arranged so as to permit gas flow between the two walls.
 6. An apparatus for forming a roving from fiber-forming thermoplastics which comprises in combination: a. the die of claim 1; b. a rod-shaped collecting means for said roving extending in a longitudinal direction through said center opening of said toroidal-shaped support means; c. drive means for rotating said collecting means.
 7. An apparatus according to claim 6 which is farther characterized by having a roving take-up means.
 8. An apparatus according to claim 6 which is further characterized by a starter sleeve means surrounding and encompassing said collecting means. 